1. Field of the Invention
This invention relates to physical quantity sensors for detecting physical quantities such as magnetism, pressure, and acceleration as well as bearing and direction of magnetism and gravitation. The present invention also relates to lead frames used for physical quantity sensors and to manufacturing methods for manufacturing physical quantity sensors using lead frames.
This application claims priority on Japanese Patent Applications Nos. 2004-263881 and 2004-374105, the contents of which are incorporated herein by reference.
2. Description of the Related Art
Recently, portable terminal devices such as portable telephones (e.g., cellular phones) have been equipped with GPS functions (where GPS stands for “Global Positioning System”) for detecting user's positional information, which is displayed on the screen of a display. GPS functions can be associated with other functions for precisely detecting geomagnetism and acceleration, whereby it is possible to detect bearings (or azimuths), directions, and movements within the three-dimensional space surrounding portable terminal devices held by users.
In order for portable terminal devices to have the aforementioned functions, it is necessary to incorporate physical quantity sensors such as magnetic sensors and acceleration sensors into portable terminal devices. In order to realize detection of bearing and acceleration within the three-dimensional space, it is necessary to use physical quantity sensor chips, which are incorporated into portable terminal devices and whose bases should be inclined by prescribed angles.
Various types of physical quantity sensors having the aforementioned functions have been developed. One type of known physical quantity sensor is a magnetic sensor, which detects magnetism but whose base is not inclined. This magnetic sensor is constituted by a first magnetic sensor chip, which is mounted on the surface of a substrate and is sensitive to magnetic factors of an external magnetic field lying in two directions (i.e., X-axis and Y-axis directions), which cross each other at a right angle therebetween along the surface of the substrate, and a second magnetic sensor chip, which is mounted on the surface of the substrate and is sensitive to a magnetic factor of the external magnetic field lying in a direction (i.e., a Z-axis direction) vertically perpendicular to the surface of the substrate. That is, the magnetic sensor measures geomagnetism factors as vectors in the three-dimensional space with reference to magnetic factors that are respectively detected by a pair of the magnetic sensor chips.
The aforementioned magnetic sensor is set up in such a way that the second magnetic sensor chip vertically stands on the surface of the substrate. This increases the total thickness (i.e., the height lying in the Z-axis direction) of the magnetic sensor. As the total thickness should be reduced to as small as possible, it is preferable to use the foregoing types of physical quantity sensors whose bases are inclined, which are disclosed in Japanese Unexamined Patent Publication No. 2004-125778, Japanese Unexamined Patent Publication No. 2004-128473, Japanese Unexamined Patent Publication No. 2002-156204, and Japanese Unexamined Patent Publication No. H09-292408, for example.
Physical quantity sensors in which physical quantity sensor chips are inclined have an outstanding advantage in that the total thickness thereof can be reduced while securing satisfactory sensitivity. For example, Japanese Unexamined Patent Publication No. H09-292408 discloses an acceleration sensor (or a physical quantity sensor) having a one-sided beam structure in which an acceleration sensor chip (or a physical quantity sensor chip) is inclined in advance with respect to a substrate; hence, even when a sensor package is mounted on the surface of the substrate, it is possible to secure a high sensitivity in a prescribed axial direction matching the inclined direction and to reduce a sensitivity in other axial directions including directions lying along the surface of the substrate.
As described above, physical quantity sensors in which physical quantity sensor chips are inclined to each other may realize mainstream technology in the future because they can reduce the total thickness to as small as possible, and they have various advantages due to inclination of chips.
FIG. 12 shows an example of a physical quantity sensor (or a magnetic sensor) in which physical quantity sensor chips are inclined to each other. Specifically, a magnetic sensor 50 of FIG. 12 is constituted by a pair of magnetic sensor chips (or physical quantity sensor chips) 51 and 52, a plurality of leads 53 for electrically connecting the magnetic sensor chips 51 and 52 to an external device, and a resin mold package 54 for integrally fixing them. The magnetic sensor chips 51 and 52 are each inclined with respect to a lower surface (or a bottom) 54a of the resin mold package 54.
In a manufacturing method of the magnetic sensor 50, the magnetic sensor chips 51 and 52 are respectively bonded onto stages 55 and 56; then, wiring using wires 57 is performed with respect to the magnetic sensor chips 51 and 52 and the leads 53. After the completion of the wiring, the stages 55 and 56 are subjected to inclination.
In the magnetic sensor 50, substantially the same length is set to the wires 57 irrespective of distances between the leads 53 and surfaces 51a and 52a of the magnetic sensor chips 51 and 52. Herein, bonding is basically performed with reference to short distances lying between the leads 53 and the surfaces 51a and 52a of the magnetic sensor chips 51 and 52. In that case, when the stages 55 and 56 are subjected to inclination, any unwanted load is applied to wires used for relatively long distances between them. This may unexpectedly break the wires 57 and may likely cause separation of the wires 57 from the surfaces 51a and 52a of the magnetic sensor chips 51 and 52. In contrast, when bonding is basically performed with reference to long distances lying between the leads 53 and the surfaces 51a and 52a of the magnetic sensor chips 51 and 52, the wires 57 may be loosened and may come into contact with each other so as to cause a short-circuit, wherein the wires 57 are likely to be exposed onto the surface of the resin mold package 54.